1. Technical Field
The present invention relates to a technique of measuring a three-dimensional shape of a surface of a measuring target.
2. Related Art
There is known a technique of measuring a surface shape (three-dimensional shape) of a measuring target by analyzing an image of the measuring target taken by a camera. As to a technique of measuring the surface shape of a mirror surface object, for example, there is a method, in which plural pieces of lighting having different features are used to take images of the mirror surface object with light reflected from the mirror surface and a normal direction of the object surface is calculated from the images (for example, see Japanese Patent No. 3553652). When the normals are obtained at a plurality of points on the object surface, the three-dimensional shape of the object surface can be restored by converting the normals into gradients to integrate the gradients (for example, see Japanese Unexamined Patent Publication No. 3-218407). As to a technique of measuring the surface shape of a diffusing object, there is a method, in which a fringe pattern is projected to the object to analyze a pattern deformation generated according to irregularity of the object surface, thereby analyzing the three-dimensional shape of the object surface. An optical cutting method, a phase shift method, and a fringe analysis method are known as typical examples of the technique of measuring the surface shape of the diffusing object (for example, see Japanese Unexamined Patent Publication Nos. 2002-286433 and 2007-196193).
In the field of an automatic measuring apparatus or an automatic inspection apparatus, there is a need to accurately measure the surface shape of the mirror surface object such as metal. For example, in soldering inspection of a board appearance inspection apparatus, there is a demand to correctly recognize the three-dimensional shape in the soldering portion in order to detect contact failure between a land and a chip or existence of a short circuit without error.